A dog's bite may be worse than its bark -- especially if the pooch isn't feeling well. A new study has determined that dogs brought to a veterinary behavior clinic for biting children most often didn't have a previous history of biting. The research, which was conducted by a team of experts from the University of Pennsylvania, School of Veterinary Medicine and The Children's Hospital of Philadelphia, found that about half of the 111 dogs in the study had preexisting medical conditions that may have triggered the lash out.

These Medical ailments that triggered lashing out included hip dysplasia (and the associated arthritic pain), compromised vision, itchiness and ear pain, says one of the study's authors, Ilana R. Reisner, DVM, PhD, DACVB, a professor of veterinary medicine at the University of Pennsylvania. Reisner cautions that the association between bad behavior and illness in half of the dogs in the study doesn't imply that medical problems were the cause of the bad behavior. Some dogs are aggressive, and that needs to be treated as a behavioral issue. But veterinary experts say it's quite common for canines that have never shown any aggressive traits to snap, bite and show other signs of agitation when they are ill -- and particularly when they have chronic conditions.

Since your pet can't speak, here's how you can read the signs that something is physically wrong with your dog before it, too, may snap.

Signs That Your Dog Is IllMost people can recognize when a canine is sick to its stomach because it may leave behind telltale visible evidence, but other ailments are much harder to detect. In addition to physical symptoms, you should look out for behavioral signs. There are two main categories of behavior that can signal red flags:

Lethargy The most common indicator that a dog isn't feeling well is not aggression -- it's depression, or lethargy, says Bonnie Beaver, DVM, past president of the American Veterinary Medicine Association and a professor at Texas A&M University. "The most common changes would be where the dog becomes less active, doesn't want to eat or eats less, tends to sleep more and tends to interact with the family less," Dr. Beaver says. "This is a common sign associated with fever, although it can be the result of other things, too, such as an upset stomach."

Aggression Another behavior that can be an indicator of a pet ailment is unusual aggression. In this sense, dogs have a lot in common with humans. "If I have a headache, I get grumpy. My fuse is shorter," Dr. Beaver says. "We don't know that dogs have headaches per se, but if they have a chronic pain, such as arthritis, or if they have an ear infection, they hurt. It eats at them. Their fuse is shorter, too." Little things that would not have bothered your pooch in the past suddenly become transgressions that merit a growl or even a snap. This is particularly of concern if children are in the household. Many children tend to want to hug, pick up or be physical with the family pet. A growl or nip may be the dog saying, "Leave me alone," says Dr. Beaver. But you should read these warning signs and take action before the interaction gets that far -- or worse.

Steps To Prevent Bad BehaviorMany dogs would never bite, snap or growl at humans, Dr. Beaver says. Like numerous other behaviors, it depends on the individual pooch, its inherent temperament, and even the background of the pet. If the dog was rescued from an abusive situation, you may not know whether the pup will respond with aggression to pain. Here are some steps that you can take to try to prevent a situation from ever getting that far.

Yearly veterinary exams These are a must to keep tabs on your pet's possible physical ailments. Dogs that come down with many diseases, such as cancer, liver problems, eye disease, etc. don't show obvious physical signs until the disease is quite advanced. Beaver recommends that you ask your veterinarian to do a complete physical exam, including blood tests, on your pet each year.

Treat ailments sooner rather than later If you see outward signs of sickness in your pup --scratching more than usual, a red "hotspot" on their body, or limping or crying when it jumps into the car -- it's important to have those symptoms treated as soon as possible. Ailments such as joint pain, ear infections or dental pain "can increase irritability," Dr. Reisner says.

Never leave small children alone with pets Pet owners need to constantly supervise whenever youngsters and pets are together. "Little kids don't mean to hurt, but they don't think. They may do things that scare or hurt the dog," Dr. Beaver says. Petting from a child may feel like slapping to the dog. And kids screaming and yelling may even frighten a pooch. "Even the most loving, trusting dog in certain situations can react," Dr. Beaver says.

Dogs should always have a quiet place to go Your home should have a place where the dog can go to escape noise, children, and other potential annoyances -- but especially when it's ill. This may be created by putting up a dog gate or by placing a dog bed in a quiet area of the basement. Make the quiet place warm, cozy and easily accessible for a sick pup. Dogs with arthritis may be uncomfortable lying down outside or on a cold floor. Similarly, walking up and down stairs to get to their escape place might be difficult.

Reisner says that her research on children who are bitten by dogs holds some important messages for dog owners -- and parents, in particular. Illness can increase the risk of aggressive behavior in dogs, even those with no predisposition to aggression. "When they're not feeling well, they need to be treated with some extra caution," she says. "Leave a dog alone if it's setting itself apart or moves away to the other side of the room. Don't let a child interact with the dog. And, if the child is too young to listen to those guidelines, put up a gate." Both dog and child may not appreciate the temporary solution, but they'll be better off because of it.